Testo 882


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Testo 882

  1. 1. www.netzerotools.comProfessional article – background articleTesto SuperResolution – the patent-pending technology for high-resolutionthermal images Testo 882 Super Resolution Testo Infrared camera Testo Thermal ImagerAbstract Testo Super ResolutionIn many industrial or trade applications, it is necessary to reliably thermograph even the smallestor extremely distant measuring objects. In such cases, the better the image resolution and themore readings in the thermal image, the more detailed and clearer the representation of themeasuring object. The Testo SuperResolution technology improves the usable, geometricresolution of the thermal image by a factor of 1.6 and provides four times more readings –comparable with a higher detector resolution. These thermal images with SuperResolutionquality, which can be conveniently viewed in the PC-based analysis software, are achieved bycombining the two technologies super-sampling and deconvolution, which can be used by Testothermal imagers thanks to a complex algorithm. The SuperResolution technology takes realthermal readings – without using a large detector and in a form that can be simply evidenced,e.g. using a slit diaphragm structure.1. IntroductionThermographers in the building industry, industrial maintenance, the electrical trade or indevelopment teams continually face similar problems: thermal analyses are required of verysmall or extremely distant objects. The structure of thermal imagers restricts their imageresolution due to the detector technology available on the market. The SuperResolutiontechnology adds a new dimension that clearly improves the image quality for thermal imagers.Thermal images taken using SuperResolution have a far higher resolution: four times morereadings and a 1.6 times better geometric resolution offer far more details on every thermalimage and thus greater reliability during every thermographic measurement. 1 www.netzerotools.com
  2. 2. www.netzerotools.comThe SuperResolution technology uses the natural hand movement to take multiple slightly offsetphotos in rapid succession. Thanks to the precise knowledge of the lens properties and use ofthe individual images in the sequence, an algorithm can be used to convert these individualphotos into a high-resolution image. The key factor here is that real readings are taken, which arecomparable to the result obtained by a higher detector resolution. This is not an interpolationprocess.2. Technological challenges of creating images of infrared radiationIn comparison to digital cameras, infrared detectors only have a low resolution. This situation isdue to both physical and technological reasons and can particularly cause problems if a userwishes to detect and measure extremely small objects. These measuring objects are even oftensmaller than a single pixel. In the worst cases, the small measuring object only makes up afraction of the entire radiation measured, which means that it may disappear into the backgroundand no longer be recognisable. If it is large enough to make up a significant portion of theradiation, the influence from the background can still tend to cause the measurement value to bebetween the temperature of the measuring object and that of the background. For themeasurement, this means that it is usually only possible to record a distorted value. This problemis particularly well-known in the field of microelectronics where thermographic images are takenof objects for which a particularly small and fine resolution is required. This challenge is alsocommon in the field of building thermography where objects can be positioned many metresaway, for example roof ridges or upper floors.3. Testo SuperResolution – the solution for high-resolution thermal imagesThe Testo SuperResolution technology makes it possible to depict more real temperaturemeasurements without using a large detector, and thus to correctly measure smaller measuringobjects. This is not a simple interpolation procedure, such as bilinear or bicubic interpolation, inwhich artificial intermediate values are generated without obtaining additional information. Suchartificially generated values can never exceed the neighbouring values – which would beparticularly necessary in the case of small objects, for example to detect hot spots. In contrast,SuperResolution increases the measurement resolution and the level of detail. The original signalbehaviour can be reconstructed (see figure 1). 2 www.netzerotools.com
  3. 3. www.netzerotools.comFigure 1: The black line represents the original signal. The white bars are original pixel values. The greybars on the left are artificially generated interpolation values – these cannot reconstruct the original signal.The orange bars on the right are SuperResolution values – these can reconstruct the original signal.Real readings are therefore calculated, which are comparable with the photo taken by an imagerwith a higher detector resolution. The geometric resolution of the SuperResolution thermal imageis clearly improved. In practice, this means that even the ‘ smallest measurable object’can be farsmaller while retaining the same distance between the thermographer and the measuring object.This means that the thermographer does not need to get closer to the measuring object yet canstill view far more details when analysing the thermal image on the PC (see figures 2 and 3).Figure 2: The image on the left shows a thermal image with 320 x 240 pixels; the image on the rightshows a SuperResolution thermal image with 320 x 240 pixels (corresponds to 640 x 480 pixels). 3 www.netzerotools.com
  4. 4. www.netzerotools.comSuperResolution offers the following advantages:- Four times as many readings in the thermal image- Geometric resolution (IFOVgeo) of the thermal image improved by a factor of 1.6- Measurable objects are 1.6 times smaller (IFOVmeas)- Far more details for PC-based analyses and thus qualitatively and quantitatively improvedevaluation options in the thermography reportTestos SuperResolution technology, for which a patent is pending, combines two well-known,recognised methods: 1) Super-sampling 2) Deconvolution‘Super-sampling’involves each photo storing a sequence of multiple, slightly offset images. Thissequence of images is then used to conduct calculations and create a higher-resolution image.The process makes use of the natural tremor (from the Latin: tremere) apparent in all humans,which results in minute movements while the thermal image is being taken. This creates asequence of images that are minimally offset from each other at random. Testos specialalgorithm uses the additional information and readings to create a higher-resolution image of thethermographed object.The ‘ deconvolution’process improves the image quality through the detailed knowledge of theinfrared lens properties. This occurs through the calculation of the imaging properties of the lenswith the thermal image. 3.1 Physical principles of the SuperResolution technology 3.1.1 Super-SamplingBolometer detectors for infrared imagers comprise a matrix arrangement of individual pixels,which absorb the radiation and convert it into an electrically evaluable signal. The pixel matrix isstored in vacuum housing for thermal insulation purposes. In turn, each pixel is made up of a thinbolometer membrane attached to fine pins over a substrate. There are small gaps between thepixels – also for thermal insulation purposes. This insulation should prevent any crosstalk, i.e. theflow of heat from one pixel to the next. However, this insulation also creates a gap between theindividual pixels in which no radiation can be detected. Furthermore, the entire pixel area is notsensitive to radiation. The radiation is only absorbed in the inner section of the pixel membrane. 4 www.netzerotools.com
  5. 5. www.netzerotools.comThis means that there are ‘ blind spots’between the pixels in which no infrared radiation isdetected. If an object is extremely small, it is possible for the signal emitted to hit such a ‘ blindspot’and thus be practically lost. The classic super sampling principle resolves this problem bymoving the entire detector matrix half a pixel width each way so that the image sequence createdis stitched to for a single image. The gaps between the pixels are therefore filled with additionalinformation and the limit frequency of the detector is improved. 3.1.2 DeconvolutionThe illustration of an object is mathematically described through the convolution (folding) of theobject radiation with the transmission function of the imager. Deconvolution is the reversal of afolding of two functions. It is therefore a mathematical algorithm which uses solely the informationabout the result of the folding – here, the output signal – and the transmission function todetermine the input signal. In our case, this means that with the output signal of the bolometerand the knowledge of the lens properties of the thermal imager, the input signal, i.e. the actualradiation of the thermographed object, is reconstructed. The result is a far sharper thermalimage. Incidentally, deconvolution also works without super-sampling. For thermographers, thismeans that their thermal images are sharper even when they are not using super-sampling, i.e.without using the natural tremor. 3.1.3 SuperResolution: super-sampling and deconvolution in oneSuperResolution is the technological combination of super-sampling and deconvolution in analgorithm and gives rise to a far higher geometric resolution of the thermal image. TheSuperResolution technology can be used to take sharper thermal images with more details andconveniently view these on a PC using the analysis software. This makes it possible to detecteven the smallest or most distant measuring objects without using a higher-cost detector. 5 www.netzerotools.com
  6. 6. www.netzerotools.com 3.2 Evidence of SuperResolution technologyIn thermography, there are several factors that play an important role in relation to the quality ofthe thermal image. Two factors of particular importance are the geometric resolution and thesharpness of the object. The improved resolution and sharpness can be seen by looking atseveral narrow slit diaphragms. In this setup, a slit diaphragm mask with vertical apertures thatgradually become smaller and closer together, is placed in front of a black panel radiator at aconstant temperature.Image without SuperResolution technologyImage with SuperResolution technologyFigure 3: trial setup with slit diaphragmWithout SuperResolution technology, you can see that the image becomes blurred as the slitsbecome more compact and closer together. The same process with SuperResolution technologyresults in an overall sharper image, in which far more details are clearly visible despite the slitsbecoming smaller and closer together.The more precise analysis shows just how problematic too low a detector resolution is:artefacts are created through aliasing and the measured temperature strongly deviates. 6 www.netzerotools.com
  7. 7. www.netzerotools.comFigure 4: Trial setup with slit diaphragm 3.3 Availability of the SuperResolution technologyThe Testo SuperResolution technology is available in all imager models in the series testo 875,testo 876, testo 881, testo 882, testo 885 and testo 890. Even thermal imagers that have alreadybeen supplied can be equipped with this technology by upgrading the imager software. 3.4 Applications of the SuperResolution technology 3.4.1 Building thermographyIn building thermography, SuperResolution technology is ideal for quickly and effectivelydetecting construction damage and analysing energy losses in buildings’heating or airconditioning systems. The high level of detail in the thermal image makes inadequate insulation,thermal bridges or construction defects clearly visible. SuperResolution thermal images aretherefore ideal for comprehensive error diagnosis and maintenance in interior areas or buildingenvelopes – especially for energy consultation purposes. 7 www.netzerotools.com
  8. 8. www.netzerotools.com 3.4.2 Electrical trade and industrial maintenanceThe SuperResolution technology makes detailed thermography easier in low, medium and high-voltage systems. High resolution thermographic images during maintenance work lead to theearly detection of defective components or connections so that the necessary preventivemeasures can be introduced in a targeted manner. This minimises the dangerous risk of fire andavoids costly production downtime. SuperResolution also enables detailed early detection ofpotential damage to production-related system components. In the case of mechanicalcomponents in particular, the discovery of thermal irregularities (e.g. due to friction or incorrectalignment) can indicate an elevated level of stress. 3.4.3 Research and developmentIn the field of research and development, high-resolution thermal images are required for thetargeted analysis of heat distribution and heat development, e.g. on printed circuit boards. Theoften tiny components can be quickly inspected in a contactless process and the smallest detailscan be thermographically depicted. All the temperature readings can then be analysed on a PCand the components thermally optimised. 4. SummaryThe Testo SuperResolution technology provides four times more readings and a geometricresolution that has been improved by a factor of 1.6 for significantly more details and thus morereliability during every thermographic measurement. From a technical perspective, this isachieved by combining two technologies: super-sampling and deconvolution. A special algorithmcombines these technologies and displays additional real readings. The higher resolution of thethermal images can be evidenced using a slit diaphragm trial setup. These far more detailedthermal images are used in many building and industrial thermography applications, both for theearly detection of damage and for more detailed analyses of thermal discrepancies. 8 www.netzerotools.com
  9. 9. www.netzerotools.comCompany profileTesto AG, with its headquarters in the Upper Black Forest, is a globally leading manufacturer ofportable and stationary measurement technology. The high-tech company offers measurementsolutions for climate and environmental technology, industrial applications, emissionmeasurement, the monitoring of food quality and the building trade, among other areas. Everyyear, the company invests approximately 15 percent of its turnover in research and developmentand thus has an above-average expenditure on future-oriented technologies.With 30 subsidiary companies and over 80 distribution partners, the company is represented allover the world, and has a worldwide staff of roughly 2200. 9 www.netzerotools.com